1613.2.5 Determination of Seismic Design Category
Structures classified as Risk Category I, II or III that are located where the mapped spectral response acceleration parameter at 1-second period, S1, is greater than or equal to 0.75 shall be assigned to Seismic Design Category E. Structures classified as Risk Category IV that are located where the mapped spectral response acceleration parameter at 1-second period, S1, is greater than or equal to 0.75 shall be assigned to Seismic Design Category F. Other structures shall be assigned to a seismic design category based on their risk category and the design spectral response acceleration parameters, SDS and SD1, determined in accordance with Section 1613.2.4 or the site-specific procedures of ASCE 7. Each building and structure shall be assigned to the more severe seismic design category in accordance with Table 1613.2.5(1) or 1613.2.5(2), irrespective of the fundamental period of vibration of the structure, T.
SEISMIC DESIGN CATEGORY BASED ON SHORT-PERIOD (0.2 second) RESPONSE ACCELERATION
| VALUE OF SDS | RISK CATEGORY | ||
| I or II | III | IV | |
| SDS < 0.167g | A | A | A |
| 0.167g ≤ SDS < 0.33g | B | B | C |
| 0.33g ≤ SDS < 0.50g | C | C | D |
| 0.50g ≤ SDS | D | D | D |
SEISMIC DESIGN CATEGORY BASED ON 1-SECOND PERIOD RESPONSE ACCELERATION
| VALUE OF SD1 | RISK CATEGORY | ||
| I or II | III | IV | |
| SD1 < 0.067g | A | A | A |
| 0.067g ≤ SD1 < 0.133g | B | B | C |
| 0.133g ≤ SD1 < 0.20g | C | C | D |
| 0.20g ≤ SD1 | D | D | D |
Where S1 is less than 0.75, the seismic design category is permitted to be determined from Table 1613.2.5(1) alone where all of the following apply:
- In each of the two orthogonal directions, the approximate fundamental period of the structure, Ta, in each of the two orthogonal directions determined in accordance with Section 12.8.2.1 of ASCE 7, is less than 0.8 Ts determined in accordance with Section 11.8.6 of ASCE 7.
- In each of the two orthogonal directions, the fundamental period of the structure used to calculate the story drift is less than Ts.
- Equation 12.8-2 of ASCE 7 is used to determine the seismic response coefficient, Cs.
- The diaphragms are rigid or are permitted to be idealized as rigid in accordance with Section 12.3.1 of ASCE 7 or, for diaphragms permitted to be idealized as flexible in accordance with Section 12.3.1 of ASCE 7, the distances between vertical elements of the seismic force-resisting system do not exceed 40 feet (12 192 mm).